In existing Digital PreDistortion (DPD) technology, the information distribution of the DPD look-up-table (LUT) is uniform quantization distribution, thus uniform quantization technology is usually used to look up an LUT address.
For a DPD system based on memory polynomial model, a math model for predistortion processing on a signal is:
                                                                        z                ⁡                                  (                  n                  )                                            =                                                ∑                                      m                    =                    0                                    M                                ⁢                                                      x                    ⁡                                          (                                              n                        -                        m                                            )                                                        ⁢                                                            ∑                                              q                        =                        1                                            Q                                        ⁢                                                                  w                                                  m                          ,                          q                                                                    ⁢                                                                                                                              x                            ⁡                                                          (                                                              n                                -                                m                                                            )                                                                                                                                                          (                                                      q                            -                            1                                                    )                                                                                                                                                                                            =                                                ∑                                      m                    =                    0                                    M                                ⁢                                                      x                    ⁡                                          (                                              n                        -                        m                                            )                                                        ·                                                            LUT                      m                                        ⁡                                          (                                                                                                x                          ⁡                                                      (                                                          n                              -                              m                                                        )                                                                                                                      )                                                                                                                                              =                                                ∑                                      m                    =                    0                                    M                                ⁢                                                      x                    ⁡                                          (                                              n                        -                        m                                            )                                                        ·                                                            LUT                      m                                        (                                                                                                                    Q                          ⁡                                                      (                                                          r                                                              n                                ,                                m                                                                                      )                                                                          )                                            .                                                                                                                              (        1        )            
The expression of LUTm(|x(n−m)|) in formula (1) is:
                                                        LUT              m                        ⁡                          (                                                                x                  ⁡                                      (                                          n                      -                      m                                        )                                                                              )                                =                                    ∑                              q                =                1                            Q                        ⁢                                          W                                  m                  ,                  q                                            ⁢                                                                                      x                    ⁡                                          (                                              n                        -                        m                                            )                                                                                                          (                                      q                    -                    1                                    )                                                                    ,                                  ⁢                  m          =                      1            ⁢                                                  .                                                  .                                                  .                                                  ⁢            M                          ,                  n          =                      1            ⁢                                                  .                                                  .                                                  .                                                  ⁢            N            .                                              (        2        )            
In formula (1), rn,m=|x(n−m)| stands for the amplitude of input signal, while Q(•) is the quantization factor. In formula (2), wmq, m=1 . . . M, q=1 . . . Q is a DPD coefficient obtained through DPD adaptive filter calculation.
Thus we can see, an input address of the LUT is decided on the basis of quantized amplitude Q(rn,m) of the input signal, that is, amplitude |x(n−m)| of the input signal is used as an index when looking up in the LUT to get the DPD coefficient, where the DPD coefficient is represented as LUTm(|x(n−m)|) in formula (1). Correspondingly, when updating the DPD coefficient, the DPD coefficient is saved with the amplitude |x(n−m)| as the index.
However, the prior art is generally applicable to a single-band DPD system. Single-band system is designed exclusively for a certain band, and a single-band LUT address is obtained by directly truncating the signal amplitude, thus unsuitable for a multi-band DPD system.